DESCRIPTION (Adapted from abstract): Registered nurses (RNs) and advanced practice nurses (APNs) play an important role in providing contraceptive services to women of reproductive age. Education and counseling regarding use, risks, and benefits of contraceptive choices are long-standing nursing interventions. With prescriptive authority, APNs are additionally responsible for providing safe, effective pharmacological interventions for preventing pregnancy. DMPA is a progestin only injectable contraception, approved for use in the US in 1992. Of concern is a potential adverse effect of DMPA on bone mineral density. Because DMPA disrupts the hypothalamic-pituitary-ovarian-axis (HPO), it theoretically will suppress estrogen production causing a relative estrogen deficiency, and corresponding loss of bone mineral density. The overall goals of this study are to determine the effect of DMPA on bone mineral density in women aged 18 to 30 years and to determine whether the effect can be modified by calcium intake or predicted by, baseline estradiol levels, irregular vaginal bleeding or weight gain. A two-year prospective longitudinal study of 275 women, 160 who are receiving their first DMPA injection, and 115 control subjects who are not using any hormonal method of contraception, will be completed. All participants will receive a baseline evaluation, and follow-up evaluations every three months for two years. At baseline, participants will have their bone mineral density of the femoral neck, lumbar spine and total body measured using dual energy x-ray densitometry (DEXA). Blood will be drawn for estradiol levels and other physical measurements completed. Participants will complete nutritional and physical activity assessments, as well as a comprehensive interview detailing demographic, medical reproductive and lifestyle behaviors that may influence bone mineral density. All participants will be given one 90-day menstrual calendar for the daily recording of vaginal bleeding. At each follow-up evaluation bone mineral density and body composition will be measured, nutrition and physical activity reassessed and components of the interview updated. The menstrual calendar will be collected, reviewed and new calendars provided. Random coefficient regression (RCR) analysis will be the major analytic strategy.